We plan to expand our hypothesis that certain metabolites of aldosterone (Aldo), present in kidney during the latent period, play significant role(s) in the regulation and/or expression of the individual renal Na+ and K+ actions of Aldo. The proposed experiments focus on the mechanisms which regulate the key sequences, subcellular sites, and specific enzymes in the metabolic pathways of Aldo in both liver and kidney, which lead to active, inactive, or potentially-active metabolites. Regulation of the key enzymes (5 alpha - and 5 beta-reductases, 3 alpha- and 3 beta-dehydrogenases, cytochrome P-450 hydroxylases, and those leading to carboxylic acids and sulfates) will be studied using (3H)-Aldo and -Ring-A-reduced intermediates in male rats, and compared to (a) females, (b) males fed low or high Na+ diet, and (c) males fed high K+ diet. Sufficient quantities of each of the polar neutral hydroxylated metabolites of Aldo (NMA) will be synthesized in liver and kidney to complete their chemical identification (by high resolution NMR, GC- and LC-Mass Spec.). Also, the further metabolism and activation/inactivation of Ring- A-reduced, NMA, 19-OH-, 19-nor-, carboxylic acid, and sulfate derivatives of Aldo will be studied (in kidney, liver and toad bladder) and the products will be isolated and chemically identified. Each derivative will be tested: (a) acutely (s.c.) and chronically (infusion) in adrenalectomized (ADX) rats for mineralocorticoid (MC) activity, and ability to enhance or inhibit individual Na+ and K+ effects of Aldo; (b) chronically in intact rats for effects and feedback on plasma renin activity and concentration, and plasma Aldo levels; (c) in ADX rats and ADX SHR for effects on blood pressure; (d) in toad bladder for ability to stimulate Na+ and H2O transport or to alter actions of Aldo or vasopressin on these processes; and (e) in rats fed either low Na+ or high K+ diet for possible enhancement of MC activities of Aldo, Ring-A-reduced and other active metabolites. Receptor interactions of these metabolites, their specific location and sites of synthesis in renal tubules, and effects on Na+, K+-ATPase will be assessed. The magnitude of key metabolic pathways in young, pre- and older, hypertensive rats (SHR and Dahl-S) will be studied. These proposed studies will highlight the importance of key metabolic pathways leading to biologically active metabolites, their physiological regulation and specific role in the mechanism of action of Aldo, and the pathogenesis of hypertension.